Grain size can be an important factor in rice milling. Size information of individual grains from a population or sample of grain or grains can be useful in determining the variations, distribution, and range of grain size. This can be used for optimization of sieve hole sizes and shapes for size sorting, which can lead to more efficient milling and higher yields and enhanced revenue. Sizing is typically performed by passing the rice grains through a sequence of sieves with different hole sizes and observing the fraction of the sample that remains behind or over each sieve.
The broken content of a sample of rice is a factor in determining the grade of a lot of rice from which the sample was taken, and therefore effects the lot price. The broken content also can be a measure used in the determination of the effectiveness and in the optimization of the rice milling process. Oblong-shaped rice grains, especially medium and long grain types, are susceptible to breakage during the milling and handling process. It is generally desirable to minimize the losses from grain breakage and over-milling, while efficiently yielding a sufficiently-milled product. The amount of broken grains, typically expressed as a percent of the total by weight, is an important factor in optimizing a rice mill.
Presently, the determination of broken content of lots of rice is performed by humans sorting samples of grains, or an approximate determination is made by processing the grains through sieves with specified hole sizes to let the smaller pieces fall through, which would include many of the broken pieces. The sieve method is not very accurate, in part because there can be a significant variation in the size of the whole grains and their shapes. Furthermore, whether an individual grain will pass through the sieve screen is a function of several other significant factors besides the size and the whole/broken classification as specified by a standard.
The manual method of sorting grains is tedious and time consuming, and the results are subject to the subjectivity of humans. The human inspectors are often highly trained and may be subject to testing and certification. Even so, there is generally a significant variation in the determination of broken content between inspectors, and a particular inspector may produce results that are biased or change over time. A less subjective, more consistent, and accurate method is desirable, so that the grading may be more consistent and fair, and so that the milling process may be altered and fine-tuned to optimize it.
Rapid, accurate, and low-cost measurement of broken content can yield advancements in milling optimization and automated process control of a rice mill. This can reduce costs and increase profits. An apparatus configured for online measurements can act as a critical sensor in controlled or automated mills or other plants.
There are various criteria and standards for determining whether a grain is broken. The US Department of Agriculture standard for rice is that the length of a piece of a rice grain must be less than 75% of its original length for it to be classified as broken. Simple length measurement is insufficient because the length of a whole small grain may be less than 75% of a large whole grain, which could result in a large percentage of grains that would have lengths within a range of lengths that are ambiguous as to whether they are broken or not.
Presently there are no automatic inspection systems that are known that can accurately determine whether a grain is considered broken or not, or determine the broken content of a sample. An apparatus that performs the inspection and analysis functions is advantageous to the rice-milling industry in particular, and can also be applied to processing and grading of other grains, seeds, food, and manufactured products.